Apparatus for anchorage of concrete reinforcements



Emma mi, 1956 F. LEONHARDT 2,763,454

APPARATUS FOR ANCHORAGE OF CONCRETE REINFORCEMENTS Filed July 24, 1955 sSheets-Sheet '1 MIDI- JNVENTOR.

Fritz Leonhard? ATTORNEY t. 1956 F. LEONHARDT ,763,4%

APPARATUS FOR ANCHORAGE 0F CONCRETE REINFORCEMENTS Filed. July 24, 19553 Sheets-Sheet 2 60 INVENTOR.

Fritz Leonhard? BY USJLM' X A TTORNE Y F. LEONHARDT APPARATUS FORANCHORAGE OF CONCRETE REINFORCEMENTS Filed July 24, 1953 5 Sheets-Sheet3 i l\ i I INVENTOR.

Fritz Leonhclrdt JITTORNEY APPARATUS FOR ANCHORAGE OF CONCRETEREINFORCEMENTS Fritz Leonhardt, Stuttgart, Germany Application July 24,1953, Serial No. 369,981 Claims priority, application Germany July 26,1952 2 Claims. (Cl. 254-29) This invention refers to a method for theanchorage of prestressed concrete reinforcements by means of separatewedges in an anchorage body and to arrangements and a jack for theexecution of this method.

A method has been known to anchor prestressed concrete reinforcements,e. g. wires or bars with threads in the structure by means of nailheads,loops or wedges. For the wedge anchorages known to date, two or morewires are spread at the anchorage point and a wedge is pushed betweenthem so that the reinforcing elements are pressed against thecylindrical surface of the opening in the anchorage plate by means ofthe wedge. By one known method, 12 and more wires are pressed with aninner wedge against the cone shaped inner surface of the anchorage blockwhich is contoured transversely to the direction of prestressing. Bydoing this, the necessary bending is constantly displaced hence thewires are twice subject to permanent deformation. Prestressing force ofthe individual wire is transferred only along a contact line at the coneshaped inside surface of the anchorage block. The aiiixed wire musttherefore be relatively long. In spite of this, with this constructionmethod the stressing wires are subject to a certain amount of slippageafter releasing the jacks before they are permanently seated.

Recently, it has also been learned to retain several reinforcingelements by means of wedges acting from outside towards inside, i. e.against an intermediate bearing body.

It is therefore an object of this invention to provide a jack foranchoring prestressing wires and rods to avoid the aforementioneddifficulties. t

It is an object to provide especially an anchorage means for reinforcingrods avoiding the necessity for threading the rods or otherwisespecially preparing them for retaining their stress.

It is a further object to provide an anchorage means for reinforcingrods without effecting a deformation of the rods.

These and other objects will become apparent in the remainder of thisspecification.

This invention consists of the following: Reinforcements in concrete arestressed by means of an apparatus resting on either the structure itselfor an anchorage plate arranged thereon and the bearing pressure is thentransferred by means of a transfer valve to wedges gripping theprestressed reinforcement on the outside with outer wedges. There isattained the advantage in one embodiment of pulling the outer wedges andthe reinforcing elements together without relative motion into a conicalopening in the bearing plate and locking them therein. Reinforcingelements may be guided in this way through the opening in the anchorageplate in a straight line so that they are not subject to permanentdeformation or bending at this point. If the reinforcement consists ofseveral similar elements, for instance wires or bars, the reinforcingelements are pressed towards one another from the outside towards theinside leaving open a central hole.

For execution of the invention, a jack is used which is States Patentice 2 equipped in such a manner that during stressing the bearing forceacts on the anchorage body and afterwards is transferred to the jawwedges.

Such a jaw may be arranged in many ways, for instance, so that ahydraulic element supplying reaction force against the prestressingtension is seated on a compound hydraulic ram and is equipped in such away that when the cylinders are emptied, it acts to seat the wedges.Also it may be arranged so that the part exerting the reaction directlyagainst the stressing force rests on another mechanism, which may bereleased by bolting it, transferring the prestressing force from thebearing plate to the tops of the wedges, causing them to seat firmly.

For practical reasons, the wedges are in such relation to thereinforcing elements that between them and the reinforcing elementsthere is circumferential contact. This permits the assembly to useshorter wedges as compared to the case of linear contact. Therefore, thewedges are lying outside of the reinforcement wire or bar group incontradistinction to the inner wedges of the known anchorage methods.Under pressure from the outer wedges, the individual elements supporteach other.

It is advantageous to increase the gripping power to contour the innersurfaces of the wedge. The contours do not have to have sharp edges, butthey may be for instance corrugated. Since there is no relative motionbetween the reinforcing elements and the wedges, the deformations,teeth, ribs or other contours grip into the material of the reinforcingelements without weakening them.

Further characteristics appear from the following description of thedrawings, it being understood that these are illustrative embodimentswhich should not be deemed limiting, the limits being determined by theappended claims.

Fig. 1 is a schematic representation of a jack double acting to carryout this invention.

Fig. 2 is a cross section through section 2-2 of Fig. 1 showing an outerwedge in circular form.

Fig. 3 is a cross section through section 3-3 of Fig. 1 showing theouter wedge in rectangular form.

Fig. 4 is a cross section through section 44 of Fig. 1 showing a roundlower wedge.

Fig. 5 is a cross section through section 5-5 of Fig. 1 showing arectangular wedge.

Fig. 6 is a cross section showing the lower wedge locked position.

Fig. 7 is a cross section of another embodiment of anchoring plate.

Fig. 8 is a cross section of a mechanical embodiment of a jack.

In the example in Fig. 1, steel anchor plate 62 is inserted into theconcrete structure which shows an opening for the wire or rod bundle 34.The concrete structure can be any of the structures known to the artthat can be reinforced by prestressed wires or rods. Stressing rods 34pass straight through opening 61 without bending. Above the opening 61the stressing rod (or rods) is surrounded by outer wedges 52. Ahydraulic jack 10 is set on the anchorage plate 62. A ring-like pistonelement part 36 is placed on the circular basic element 42 of the jackresting on anchorage plate 62. Between parts 36 and 42 circular chamber48 is formed presenting a hydraulic cushion. The chamber is sealed tothe outside by gasket 44. Inside the chamber, springs 46 are arranged,which hold apart parts 36 and 42. Circular chamber 48 is connected bypipe 54, pressure gauge 56 and valve 53 to an external chamber (notshown) for holding a small supply of hydraulic fluid with means forforcing the hydraulic fluid into chamber 48 under pressure. On ringpiston 36 there is a ring cylinder 12, which forms in relation to ringpiston 36 a pressure chamber 20, inasmuch as hydraulic fluid may beforced in by way of channel 24, controlled by valve 28 and pressuregauge 26 and means for forcing the hydraulic fluid into chamber 20 underpressure. Ring piston 36 and ring cylinder 12 are sealed towards eachother by gaskets 22. The intermediate piece 18 of the ring cylinder 12is provided with a borehole which has a conically widening part 30 andthrough which the stressing rods 34 pass in line with the anchorageopening 61. Within the conical parts 30 of the opening the stressingrods are surrounded by pinch wedges 32.

If a hydraulic fluid is admitted under pressure through pipe 24, thistries to press the ring cylinder 12 in Fig. 1 upwards. Thus the wedges32 are pushed towards the stressing rods 34 and the latter are pushedtowards one another so that the stressing rods are stressed when moreliquid is forced in which make them elongate elastically. The elongationis increased over and beyond the amount necessary for the working stressto the extent that a small movement backwards of the ring piston 36 forattaining the gripping of the stressing wires in or on the anchorageplate 62 is possible without the stress decreasing beneath the requiredmeasure. During the stressing the ring piston 36 rests on the liquidcontaining cushion formed in chamber 48. The valve 58 is closed. Priorto stressing the valve 58 was opened long enough for the ring piston tosit on the wedges 52. If the valve 58 is now opened so that thehydraulic fluid may flow into the storage chamher (not shown) thepressure force in chamber 20 acts through ring piston 36 onto outerwedge 50 so that it is forced down over inner wedge 52 causing thelatter to be anchored firmly to the rods 34. Figure 6 shows the wedgesin locked position. Thereafter the pressure liquid supply is released atvalve 28 so that the stressing wedges 32 may be removed. Then the jackmay be lifted from the anchorage plate 62. The springs 46 force theparts 42 and 36 apart again when the jack is removed as soon as thevalve is opened again, this movement being limited to such degree thatring piston 42 cannot be completely pushed out from ring piston 36.

The outer wedges surrounding the stressing elements, i. e. both wedges52 as well as wedges 32 may have the greater cross section representedby ribs or corrugations which under pressure are impressed into thereinforcing elements they grip.

It is possible to guide the stressing elements individually throughseparate openings in the anchorage plate. In this case everyprestressing element is surrounded by its own outer wedge which could bea conical casing slit on one side. However, several wedges may also beplaced around the individual elements.

Figure 3 shows an alternative embodiment for upper Wedges 32 in whichrectangular wedges 32c and 32d are used.

The lower wedges 52 may also be rectangular as shown by wedges 52c and52d in Figure 5.

With the example in Fig. 1 it is assumed that anchor plate 62 ended withthe outside surface of the structure 60. However, it is also known thatthe anchor plates may be sunk in the structure 60 and to cover it withconcrete as shown in Fig. 7. The anchorage method which is the subjectof the invention may also be used advantageously with a covered anchorplate.

The jack in Fig. 8 is formed in the same manner as Fig. l inasmuch as itcan rest, if so chosen, on either the anchorage body or on the clampwedges. Also here the load is so transferred that the clamping wedgesare seated by the stressing force when the counterforce supporting thejack is transferred from the anchorage body to the wedges afterstressing. While, however, with jack in Fig. 1 the jack elementsupplying the supporting force against the stressing for pressure wasresting on a hydraulic element, in construction method according to Fig.8 the corresponding jack part rests on de-boltable apparatus, forinstance on a secured and releasable steep spiral and is formed in sucha manner that it seats the clamping wedges if this support is released.

The inside part 121 of the section 117 has at the lower end spiral 147on which a stressing head 146 is screwed on. The conical inner bore holeof this stressing piece contains the stressing wedges 124 which areretained at the cone enclosure surface by a pressure spring 148 which isinserted between the inner parts 121 and the wedges.

The ring piston 19 rests on an inner ring 149 which is retained on ananchorage ring 150. The inner ring 149 is screwed onto anchorage ring150 by means of a steep multi-thread spiral, preferably trapezoidalspiral. The pitch is so great that there is no excessive friction. Ringpiston 19 has at its lower part spiral 152 which is selflocking and towhich a safety ring 153 is screwed, and resting on anchorage 150 whichprevents the ring piston 19 with inner ring 149 from slipping downwardon spiral 151 inside the anchorage ring 150 when fluid pressure ispumped into the pressure chamber 118 between ring pisten 19 and ringpiston 117. There are one or more wedges set into the opening providedin anchorage plate 262 the thickness of which wedges increase in theexample in the drawing and forms a flange 145. If the retaining ring 153is screwed up ring piston 19, the pressure in chamber 118 due to thetension in the reinforcing elements will cause the member 149 to traveldownwards in the spiral guides 151 until piece 149 rests on the flange145 of the wedges 160.

This force causes the wedges 160 to seat and grip the reinforcingelements 34. Thereafter the stressing wedges 124 may be released in thesame manner as has been described for the wedges of the jack inFigure 1. The bearing area of the ring piston 19 with the inner ring 149is formed in such a manner that a turning movement between these twoparts remains possible without the ring piston 117 turning also. Ifnecessary, a roller bearing may be placed between these two parts.Otherwise, the dimensions have to be so chosen that the loweringmovement to clamp the wedges 160 does not release more than a minor partof the stress in the reinforcing elements 34.

The back surfaces at the outer wedges do not necessarily have to becarefully finished to reduce friction.

In addition to the type wedges shown, any other suitable wedges may beused. The bearing plate may have, for instance, a conical openingsimilar to opening 30 in Figure 1, and a wedge similar to that shown as32 in Figure 1 may be used. The wedge 32 shown in Figure 1 may besubstituted by a wedge combination 5052, with wedge 52 being seated by ahammer, etc.

I claim:

1. A jack of the class described comprising a cylinder and a pistoncoacting therewith, a hydraulic chamber between them for forcing themapart, said chamber connected to a source of hydraulic fluid and meansfor forcing the hydraulic fluid into the chamber under pressure, a borehole in the cylinder for passing therethrough material to be jacked,means for securing such material to the cylinder, a retractable ringmounted in the piston and of length suflicient to project therefrom andact as a bearing surface for the piston, means for holding the ring inan extended position, means for permitting retraction of the ring intothe piston and a receptacle in the piston adjacent the retractable ringand surrounding the bore hole for holding and seating a wedge around thematerial to be jacked.

2. A jack of the class described comprising a cylinder and a pistoncoacting therewith, a hydraulic chamber be tween them for forcing themapart, said chamber connected to a source of hydraulic fluid and meansfor forcing the hydraulic fluid into the chamber under pressure, aborehole in the cylinder for passing therethrough material to be jacked,means for securing such material to the cylinder, a retractable ringmounted in the piston and of length sufl icient to project therefrom andact as a bearing surface for the piston, a hydraulic chamber between thepiston and the ring, a container for hydraulic fluid connected to thechamber, a spring for holding the ring in an extended position and areceptacle in the piston adjacent the retractable ring and surroundingthe bore hole for holding and seating a Wedge around the material to bejacked.

References Cited in the file of this patent UNITED STATES PATENTS1,312,009 Thrift Aug. 5, 1919

